MIX PROPORTIONING

1. 1
Kandahar University
Engineering Faculty
Civil Department
MIX PROPORTIONING
Abdul Habib “Zaray”

2. Methods of Concrete Mix Design
I.S. Method
British Method
A.C.I. Method etc.
> these methods are based on two assumption
a: Compressive Strength of Concrete is governed by its Water-
Cement Ratio
b: Workability of Concrete is governed by its Water Content
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3. Outline
Design consideration:
a: obtaining good workability
b: Prevent segregation and bleeding
c: Adequate durability
Measuring workability, Slump
Guidelines We Use For Mix Design
ACI Standard Mix Design Method
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4. DEFINITION
The process of selecting suitable
ingredients of concrete and determining
their relative quantities with the objective
of producing a concrete of the required
strength, durability, and workability as
economically as possible, is termed the
concrete mix design
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5. Obtaining Good Workability
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Workability: the ease with which the
concrete ingredients (gravel, sand , cement,
water) can be mixed, transported, placed,
consolidate, and finished with minimum
loss of homogeneity

6. Obtaining Good Workability..Cont...
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7. Obtaining Good Workability
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8. Obtaining Good Workability
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9. Prevent Segregation & Bleeding
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Segregation: the tendency for the gravel
particles to separate from the rest of the
ingredients.
Bleeding: the tendency for the mixing
water to separate from the rest of the
ingredients.

10. Well Graded Aggregates Will Reduce
Segregation & Bleeding
Well Graded Poorly Graded
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11. Measuring Workability: Slump
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12. The Slump Cone
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13. Approximate Required Slump
Values
Concrete
Construction
Slump (Max.) Slump
(Min.)
Reinforced foundation
walls/footings
3 in 1 in
Plain footings and
substructure walls
3 in 1 in
Beams & reinforced walls 4 in 1 in
Building columns 4 in 1 in
Pavement & slabs 3 in 1 in
Mass concrete 2 in 1 in
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14. Economics of Mix Design
Goals:
Maximize strength
= minimize water
= control bleeding & segregation
Reduce Cost
= use largest gravel possible for the job
= minimize paste requirement
Provide good durability
= use well graded aggregates
= maximize void packing
= reduced segregation
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15. Guidelines We Use For Mix Design
PCA Manual
• Tables for w/c ratio based on compressive strength
requirement & slump (workability)
• Volume of stone required based on max. agg. size and
sand fineness.
• Water required based on max. agg. size, slump & w/c
ratio (compressive strength)
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16. Design Method We Will Use:
Absolute Volume Method
Assumes no air voids in concrete
Amount of concrete is sum of solid volumes:
1 CUBIC YARD
• Cement
• Sand
• Coarse aggregate
• Water
• Air
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17. Water Correction
Any water content in aggregates above SSD
water content must be subtracted from the
water requirements
Any water requirement of aggregates
(below the SSD water content) must be
added to the water requirements
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18. Material Values & Constants
Needed For Design:
SSD (Absorption) of Sand
Unit Weight & SG of Sand
SSD (Absorption) of Stone
Unit Weight & SG of Stone
Density of Cement = 195 pcf
SG Cement = 3.15
Density of Water = 62.4 pcf
1 Cubic Foot Water = 7.48 gal
1 Gal. Water = 8.34 lbs
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19. The standard ACI mix design procedure can
be divided up into 8 basic steps:
1. Choice of slump
2. Maximum aggregate size selection
3. Mixing water and air content selection
4. Water-cement ratio
5. Cement content
6. Coarse aggregate content
7. Fine aggregate content
8. Adjustments for aggregate moisture
ACI Standard Mix Design
Method
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20. Step #1: Select Slump
Table 9.6
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21. Step #2: Determine Mixing Water and Air Content
Table 9.5
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22. DEFINITION: Nominal maximum aggregate size is the largest sieve that retains
some of the aggregate particles.
ACI Limits:
1/3 of the slab depth
3/4 of the minimum clear space between
bars/form
1/5 minimum dimension of non-reinforced
member
Aggregate larger than these dimensions may be difficult to consolidate
and compact resulting in a honeycombed structure or large air pockets.
Step #3: Max. Agg. Size Check
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23. Step #4: Select W/C Ratio
Table 9.3
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24. Step #5: Cement Content
The calculated cement amount is based on
the selected mixing water content and
water-cement ratio.
W/C= Wt. of Water
Wt. of Cement
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25. Step #6: Coarse Agg. Content
Table 9.4
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26. Step #7: Fine Agg. Content
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27. Step #8: Batch Weight & Water Adjustment
Aggregate weights.
Aggregate volumes are calculated based on oven dry unit weights, but aggregate is
batched in the field by actual weight.
Any moisture in the stockpiled aggregate will increase its weight.
Without correcting for this, the batched aggregate volumes will be incorrect.
Amount of mixing water.
If the batched aggregate is anything but saturated surface dry it will absorb water
(if dry) or give up water (if wet) to the cement paste.
This causes a net change in the amount of water available in the mix and must be
compensated for by adjusting the amount of mixing water added.
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28. Mix Design Example:
10” Thick Unreinforced Pavement Slab
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29. Properties of Concrete
Specified By Engineer:
Slump =1.0 inch
28-day strength of 5000 psi
Air content: 4.5 - 6.5 percent
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30. Information About Materials:
Coarse aggregate we are using (ODOT #467):
• nominal maximum size = 1.5 inch (see Agg. Size Table)
• dry-rodded weight = 100 lb/ft3
• specific gravity = 2.68
• moisture content = 1.0 percent
• absorption = 0.5 percent
Fine aggregate:
• fineness modulus = 2.80
• specific gravity = 2.64
• moisture content = 5 percent
• absorption = 0.7 percent
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31. Step #1: Select Slump
Engineer Specified 1” (correlates w/table)
WE ARE DESIGNING BATCH WEIGHTS FOR ONE CUBIC YARD
Table 9.6
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32. Step #2: Determine Mixing Water and Air Content
1.5” Stone
1” Slump
Table 9.5
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33. Weight of Water = 250 lbs/yd3
Volume of Water = 250 lbs/yd3 = 4 ft3
62.4 lbs/ft3
Volume of Water = 4 ft3 per cubic yard of concrete
Step #2: Determine Mixing Water and Air Content
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34. ACI Limits:
1/3 of the slab depth
10”/3 = 3.33 inches > 1.5” OK
Step #3: Max. Agg. Size Check
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35. Step #4: Select W/C Ratio
Table 9.3
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36. Step #5: Cement Content
W/C= Wt. of Water
Wt. of Cement
Wt. of Cement = 250 lbs/yd3
.40
=625 lbs/yd3
Volume of Cement = 625 lbs/yd3 (Concrete)
3.15 x 62.4 lbs/ft3
Volume of Cement = 3.18 ft3 per cubic yard of concrete
SG Cement
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37. Step #6: Coarse Agg. Content
Table 9.4
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38. Step #6: Coarse Agg. Content
Weight (Dry) =.71 x 27 ft3/yd3 x 100 lb/ft3 = 1,917 lbs
Volume = 1,917 lbs = 11.46 ft3
2.68 x 62.4 lbs/ft3
Dry Rodded Unit Wt of Stone
SG Stone
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39. Step #7: Fine Agg. Content
27 ft3 Cubic Yard of Concrete
4 ft3 Water
1.49 ft3 Air (.055 x 27 ft3)
3.18 ft3 Cement
11.46 ft3 Stone
6.87 ft3 Sand
Wt of Sand(Dry) = 6.87 ft3 x 2.64 x 62.4 lbs/ft3 = 1,131.7 lbs.
SG Sand
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40. Step #8: Aggregate Batch Weights & Water Adjustment
Since there is moisture in both coarse & fine aggregate,
their batch weights must be adjusted
Wt of Stone(Wet) = 1,917 lbs x 1.01= 1,936.2 lbs
Wt of Sand(Wet) =1,131.7 lbs x 1.05= 1,188.3 lbs
1% Moisture
5% Moisture
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41. Mixing water needs to be adjusted. Both the coarse and fine aggregate are
wet of SSD and will contribute water to the cement paste.
Water from Stone = 1,917 lbs. x (.01-.005) = 9.59 lbs
Water from Sand= 1,131.7 lbs x (.05-.007) = 48.66 lbs
Water = 250 lbs – 9.59 lbs – 48.66 lbs = 191.75 lbs
Step #8: Aggregate Batch Weights & Water Adjustment
MoistureDry Wt. Absorption
Dry Wt. Moisture Absorption
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42. Final Batch Wts. (1 Cubic Yard)
Water 191.75 lbs = 23 gallons
Cement 625 lbs
Stone 1,936.2 lbs
Sand 1,188.3 lbs
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43. BS Method > Example
10” Thick Unreinforced Pavement Slab.
Characteristics obtained by engineer:
Slump =1.0 inch
28-day strength of 5000 psi
Air content: 4.5 - 6.5 percent
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44. BS method cont.…
Step 1: target mean strength
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45. BS method cont.…
Step 2: water cement ratio
w/c=
0.48
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46. BS method cont.…
Step 3: the cement content
Water content = 190kg/cum
Cement content = 160/o.48 = 334kg/cum
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190

47. BS method cont.…
Step 4: total aggregate content
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48. BS method cont.…
Water content = 160kg/cum
Specific gravity = 2.68
Fresh density of concrete = 2500kg/cum
Total aggregate content = 2500 – 334 – 160 =
2006kg/cum
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49. BS method cont.…
Step 5: the proportion of fine aggregate is
32% hence fine aggregate content is
F.A = 0.32 * 2006 = 641kg/cum
C.A = 2006 – 641 = 1365kg/cum
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50. BS method cont.…
Water = 160kg
Cement = 334kg
F.A = 641kg
C.A = 1365kg
Total = 2006kg/cum
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